Numerous proposals have been made heretofore for equipment suitable for handling fluent particulate material from a bulk source and conveying this material in a continuous regulated stream to a point of use. Many of these machines make use of a pressurized gaseous stream as a material suspension and conveying medium. This transport mode requires suitable means for introducing the fluent material into the pressurized stream from a bin or other supply source subject to atmospheric pressure. A commonly utilized technique makes use of a continuously pressurized material dispensing chamber replenished from time to time from another normally pressurized chamber temporarily ventable to the atmosphere while being refilled from a supply source. Such equipment requires the use of flow control valves and operating means therefor operated in some predetermined sequence.
Ridley U.S. Pat. Nos. 2,949,275 and 3,090,593 each show material handling equipment utilizing manually controlled valves between the several fluent material handling chambers. Such equipment is relatively simple but requires skilled operators who pay strict attention to operating requirements and the need for manually controlling the several valves in proper sequence. Ryan U.S. Pat. No. 2,138,356 discloses a bag filling and weighing apparatus in which the various valves are controlled and operated electrically by a programming timer. The Kirchhoefer U.S. Pat. Nos. 3,190,509 and 3,315,824 also show automatically operated fluent material handling equipment using a timer to control solenoid operated valves in proper sequence. Such systems have the distinct disadvantage of requiring a source of electrical power not always available on construction projects. Moreover, electrical equipment exposed to the weather and to water typically encountered on construction projects pose hazards to the workmen and require special and expensive insulation safeguards. Domina U.S. Pat. Nos. 1,943,589 and 1,979,320 avoid the hazards and shortcomings posed by electric controls for fluid handling equipment and instead utilize pneumatically powered controls. However, his main control valve is driven through complex gear reduction mechanism from the motor operating the feeder for the material dispensing chamber. This expedient provided no assurance that the dispensing chamber will be refilled timely. Moreover, all of these prior machines are unnecessarily complex, bulky and costly to service and maintain.